Not only do you get inheritance for your web pages, they actually execute faster. Why? Because includes require extra overhead of setting up "mock" requests in which the included ASP scripts are executed. MasterPages do not require this extra work.

If you were to simply use /handlers/user.login, that one handler would be invoked for any website's /handlers/user.login URI. Unless this is what you want, avoid the namespace clashes by going with the naming convention described above.